By Chris Oddo

(February 21, 2013) -- 20-year-old American Jack Sock won a spirited battle over James Blake at the U.S. National Indoors on Thursday evening, 7-5, 6-4, to reach his second career ATP quarterfinal.

Just a day after upsetting second-seeded Milos Raonic for his biggest career victory, Sock was pushed to the brink by Blake, who is 13 years the Nebraska native's senior and also his partner in the doubles draw this week (they defeated the No. 2 seeds in the first round).

In a wild first set that lasted over an hour, Sock, currently ranked No. 168 in the world, saved all nine break points he faced against Blake, including five set points in a wild tenth game.

Sock fell behind triple break point before digging himself out with clutch serving against an extremely pesky Blake. "You never feel comfortable serving against James, because he hits the ball so clean and takes the ball so early," said Sock. "Even when you feel like you are hitting big serves he can just rip a winner off of everything. He was doing that a couple of times on my game points, and I was missing a couple of shots I probably shouldn't have missed, and giving some loose points away on the game points, but in the end I was able to change up my positioning and change up my serve a little bit to try to take him out of his rhythm."

After striking his first of four aces on the evening to close out the marathon game, Sock would benefit from a Blake double fault a few minutes later to take a 6-5 lead.

While serving out the set in the next game, Sock would save another two break points. With Blake applying pressure on his second serve as much as he could, Sock failed to convert on five set points before finally taking the opener, 7-5.

In the second set Sock earned a break point with a deft lob in the first game, and converted with a tasty drop shot to lead 1-0.

Blake would break back earn his lone break of the evening to level thing at one-all, but Sock would bounce back right way, securing his third break on the evening to take a 3-2 lead.

Blake would breeze through his next two service games to keep it close, but Sock’s serving was too strong down the stretch. He did not allow the 33-year-old wildcard another look at a break point, and even though he failed to convert his first match point in the tenth game, he lashed a forehand to the open court to force Blake’s final error and close the victory out in one hour and forty-eight minutes.

"I always love coming to this tournament," said Sock. "The ball always feels some good for some reason on that court out there."

The former U.S. Open mixed doubles champion will bid to reach his first career singles semifinal on Friday when he faces Spaniard Feliciano Lopez. Lopez moved through when Tommy Haas withdrew from their second round match with a viral illness.

In other second-round action on Thursday, Marin Cilic saved three match points to squirm past Igor Sijsling 7-6(2), 3-6, 7-6(7), while Americans Sam Querrey and Donald Young were defeated.

Querrey, the No. 2 American behind John Isner, went down in three sets against Marinko Matosevic of Australia 6-3, 4-6, 7-5, while Young was blitzed by Japanese sensation Kei Nishikori, 6-3, 6-3.

Elsewhere, seventh-seeded Alexandr Dolgopolov defeated American Rhyne Williams 6-4, 4-6, 6-4, and Uzbekistan’s Denis Istomin demolished Lleyton Hewitt, 6-1, 6-2.

(Photo Credit: AP)